A synopsis of this book is rather beside the point, but here goes. Dylan lives with his sisters and parents, and is the only boy in a small, rainy town in Wales. They run a small garage, the Snowdonia Oasis Auto Marvel, on the brink of insolvency. Dylan is obsessed with the Teenage Mutant Ninja Turtles, as is Tom, the man who tried to rob them, and whom they hire instead.
Then a series of seemingly unrelated events starts to change things in their lives and community. A car they bought to fix and sell disappears, and soon after so does their father. A group of men in vans moves into the abandoned quarry on top of the mountain where, it turns out, they are storing art from the National Gallery to protect the pieces from floods in London. And their leader, hearing that Dylan has named his chickens Donatello and Michaelangelo (after the Turtles), thinks Dylan is an art genius. But it's really his younger sister who's a genius, as she shows when she plans a heist of one of the paintings hidden in the quarry.